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Southeastern Bering Sea 2024 Report Card

For more information on individual Report Card indicators, please see ‘Description of the Report Card indicators’ (p. 237). For more information on the methods for plotting the Report Card indicators, please see ‘Methods Description for the Report Card Indicators’ (p.241).

* indicates Report Card information updated with 2024 data.

*North Pacific Index (Nov-Mar average)

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  • *The North Pacific Index (NPI) effectively represents the state of the Aleutian Low Pressure System. Above average (below average) winter (Nov-Mar) NPI values imply a weak (strong) Aleutian Low and generally calmer (stormier) conditions. The NPI was average during winter 2023–2024 (Figure 12) that may partially explain the near-normal sea ice extent.

*Sea Ice Extent

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  • *The mean sea-ice extent over the southeastern Bering Sea shelf (south of 60°N) was at the long-term mean (1985–2024) in 2024 (ice year defined as 1 Sept to Aug 31). Seasonal sea- ice extent has implications for the cold pool, spring bloom strength and timing, and bottom-up productivity.

*Cold Pool Extent

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  • *The areal extent of the cold pool in the eastern Bering Sea (EBS), as measured during the bottom trawl survey (Jun-Aug; including strata 82 and 90; 1982–2024), was just below the time series average in 2024. The 2024 extent (156,800 km2) was 12.7% smaller than 2023.

*Proportion of Open Water Blooms

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  • *The proportion of open water blooms in the southeastern Bering Sea (south of 60°N) was 62.5% during 2024, similar to 2023,and just below the time series average (1998–2024). 2024 had fewer open water blooms than during the warmer period 2014–2021, but higher than during the cold period 2007–2012. A higher proportion of ice-associated blooms is correlated with higher abundances of large zooplankton (Hunt et al., 2011).

*Large Copepod Abundance

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  • *The abundance of large copepods (predominantly Calanus spp.) as measured during August/September along the 70 m isobath over the southeastern shelf, peaked in 2008 and 2012 during cold years, but has remained below the time series mean (2000–2024) since 2015.

*Euphausiid Biomass

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  • *An acoustic estimate of euphausiid density increased from 2018 through 2022, but declined to the second-lowest value in the time series in 2024.

*Pelagic Forage Fish (kg/km2)

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  • *The density of pelagic forage fish (i.e., age-0 pollock, age-0 Pacific cod, herring, capelin, rainbow smelt, saffron cod, and all species of juvenile salmonids) sampled by surface trawl over the southeastern Bering Sea shelf in late-summer (Aug-Sep; 2003–2024) peaked in 2005, was below the time series average in 2008–2012, was above average in 2014, 2016, and 2018, but dropped to below the long-term mean in 2024. The trends are dominated by age-0 pollock and juvenile sockeye salmon; in 2024 the densities of both were low.

*Motile Epifauna Biomass (fish and invertebrates 1000t)

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  • *The biomass of motile epifauna measured during the standard bottom trawl survey (Jun-Aug; 1982–2024) increased from 2023 to 2024 and remains above the long term mean. Collectively, brittle stars, sea stars, and other echinoderms have accounted for more than 50% of the biomass in this guild. Brittle stars alone have accounted for more than 30% of motile epifauna biomass since 1997. Brittle stars have trended downward since their peak biomass in 2016 but remain above their long-term mean. The biomass index sharply increased for tanner crabs and snow crabs, while king crabs remain below their long term mean.

*Benthic Forager Biomass (fish 1000t)

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  • *The biomass of benthic foragers measured during the standard bottom trawl survey (Jun-Aug; 1982–2024) increased 10% from 2023 to 2024 but remain below the time series mean. The biomass of flathead sole, northern rock sole, and yellowfin sole all contributed to the increasing guild index. However, both northern rock sole and yellowfin sole remain below their long-term means.

*Pelagic Forager Biomass (fish 1000t)

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  • *The biomass of pelagic foragers measured during the standard bottom trawl survey (Jun-Aug; 1982–2024) increased 71% from 2023 to 2024 to just above their long-term mean. The biomass of the pelagic forager guild was generally stable from 2016 to 2019, but dropped to their third lowest value in 2021. The trend in the pelagic forager guild is largely driven by walleye pollock who on average account for 68% of the biomass in this guild. In 2024, the index for pollock increased 78% from 2023. Among species of secondary importance, Pacific herring have decreased 5% from 2023, but remain above their long-term mean.

*Apex Predator Biomass (fish 1000t)

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  • *The biomass of apex predators measured during the standard bottom trawl survey (Jun-Aug; 1982–2024) in 2024 is nearly equal to their value in 2023 and is below their long term mean. The trend in the apex predator guild is largely driven by Pacific cod, which decreased 5.5% from 2023, and is also influenced by arrowtooth flounder, which increased 26% from 2023.

*Multivariate Seabird Breeding Index

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  • *The multivariate seabird breeding index indicated that seabird reproductive timing and success at the Pribilof Islands was slightly below average in 2024, although there were differences between islands and species that may reflect local-scale processes and/or diversity in foraging strategies. Reproductive success and/or hatch timing can be influenced by their food supply, therefore below-average values may indicate lower than average recruitment of year classes that seabirds feed on (e.g., age-0 pollock), or lower than average supply of forage fish that commercially fished species feed on (e.g., capelin eaten by both seabirds and Pacific cod).

*Borealization Index

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  • *The borealization index (1972–2024) describes the transition from an Arctic physical state supporting a cold-adapted species assemblage to a subarctic (boreal) physical state supporting a warm-adapted assemblage. Arctic-like conditions occurred in the 1970s and 2007–2013. Boreal conditions occurred during the warm, lower-ice years of 2014–2021. The borealization index has returned to values similar to the time series mean during 2022–2024.

Northern Bering Sea 2024 Report Card

* indicates Report Card information updated with 2024 data.

*North Pacific Index

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  • * The North Pacific Index (NPI) effectively represents the state of the Aleutian Low Pressure System. Above average (below average) winter (Nov-Mar) NPI values imply a weak (strong) Aleutian Low and generally calmer (stormier) conditions. The NPI was average during winter 2023–2024 (Figure 12) that may partially explain the near-normal sea ice extent.

*Sea Ice Extent

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  • *The mean sea-ice extent over the northern Bering Sea shelf (north of 60°N) has been increasing since the time series (1985–2024) low ice extent in 2018 (ice year defined as Sept 1 to Aug 31). Sea ice extent was above average in 2024. Seasonal sea-ice extent has implications for the cold pool, spring bloom strength and timing, and bottom-up productivity.

Cold Pool Extent

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The areal extent of the cold pool in the northern Bering Sea (NBS), as measured during the bottom trawl survey (Jun-Aug; strata 70, 71, and 81; 2010, 2017, 2019, 2021–2023), decreased between 2010 and 2019, but returned to the time series average in 2023. The 2023 extent (83,797 km2) was similar to 2022.

*Proportion of Open Water Blooms

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  • *The proportion of open water blooms in the northern Bering Sea (north of 60°N) was about 1.4% during 2024, which is the lowest value since 2008. A higher proportion of ice-associated blooms is correlated with higher abundances of large zooplankton (Hunt et al., 2011).

*Large Copepod Abundance

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  • *The abundance of large copepods (predominantly Calanus spp.) as measured during August/September over the northern shelf, peaked in 2011 during a cold year, and has remained near the time series mean (2000–2024) since 2021.

*Pelagic Forage Fish (kg/km2)

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  • *The density of pelagic forage fish (i.e., age-0 pollock, age-0 Pacific cod, herring, capelin, rainbow smelt, saffron cod, and all species of juvenile salmonids) sampled by surface trawl in late- summer (Aug-Sep; 2003–2024) peaked in 2004 and 2014 and remained above average through 2019, then dropped to below the long-term mean in 2021–2024. The trends are dominated by age-0 pollock and herring; in 2024 the densities of both were low.

Juvenile Snow Crab Estimated Biomass (metric tons)

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  • The biomass of juvenile snow crab measured during the northern Bering Sea bottom trawl survey (2010, 2017–2019, 2021–2023) peaked in 2010 and decreased through 2023, with a smaller peak in biomass in 2022. The trend in juvenile snow crab biomass (combination of small male and immature female crab) reflects benthic production of the ecosystem and is a signal for future crab recruitment into the eastern Bering Sea.

Yellowfin Sole Estimated Biomass (metric tons)

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  • The biomass of yellowfin sole observed during the northern Bering Sea bottom trawl survey (2010, 2017, 2019, 2021–2023) plateaued from 2019–2022 and then decreased in 2023. Trends in yellowfin sole biomass reflect relative predation pressure on small infaunal prey (e.g., polychaete worms, bivalves, small crustaceans).

Walleye Pollock Estimated Biomass (metric tons)

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  • The biomass of walleye pollock observed during the northern Bering Sea bottom trawl survey (2010, 2017, 2019, 2021–2023) peaked from 2017–2019 and decreased through 2023. Trends in walleye pollock biomass reflect relative predation pressure on zooplankton and forage fish.

Pacific Cod Estimated Biomass (metric tons)

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  • The biomass of Pacific cod observed during the northern Bering Sea bottom trawl survey (2010, 2017, 2019, 2021–2023) peaked in 2019 and then decreased through 2023. Trends in Pacific cod biomass reflect relative predation pressure on forage fish and crab.

Key

  2019-2023 Mean   2019-2023 Trend
  1 s.d. above mean   increase by 1 s.d. over time window
  1 s.d. below mean   decrease by 1 s.d. over time window
  within 1 s.d. of mean   change <1 s.d. over time window
  fewer than 2 data points   fewer than 3 data points